A samara is a simple dry fruit composed of a seed encased in an ovary wall that extends into a flattened wing or wings. The wings of samaras allow them to be carried by the wind when falling from their parent trees or plants. Maple seeds are a single-wing type of samara.
In aeronautical terms, a maple seed may be described as an “auto-rotating helicopter.” When a maple seed falls from the tree on which it developed, it picks up speed and starts to rotate around its center of mass. The shape of the wing causes the airflow around the samara (as it drops through the air) to induce a spinning motion. The maple seed is described as “auto-rotating” because its spinning helicopter-like motion arises automatically as it falls through the air.
This auto-rotation provides a slow gliding descent in the presence of wind, allowing the maple seed to be carried by the wind away from its parent tree. The same gust of wind that causes the seed to break free of the tree may then carry that seed away. The maple seed has a relatively high “glide ratio” (the distance covered horizontally over distance dropped vertically) in the presence of wind, and therefore stays in the air longer and can travel further away from the parent tree than a typical seed or nut dropped through the air, thus providing a greater chance for the dispersal and propagation of the species.
Maple seeds and other samaras have inspired inventors and designers ever since human-powered flight was proven to be possible. Engineers and researchers have explored the nature of maple seed flight in order to understand it and adapt it to various technological applications. For example, recent published research, led by David Lentink, an assistant professor at Wageningen, and Michael H. Dickinson, the Zarem Professor of Bioengineering at Caltech, revealed that, by swirling, maple seeds generate a tornado-like vortex that sits atop the front leading edge of the seed's wing as it spins slowly to the ground. This leading-edge high-turbulence vortex lowers the air pressure over the upper surface of the maple seed, effectively exerting pressure on the wing in the opposite direction that gravity is pulling it, thereby giving it some lift to counteract gravity's pull. This vortex provides the maple seed approximately twice the lift generated by non-swirling gliding seeds. See, e.g., http://www.popsci.com/military-aviation-amp-space/article/2009-06/inspired-spinningmaple-seeds-tested-robofly; http://www.youtube.com/watch?v=ce2HUKizMTw (confirmed 19 Dec. 2010).
Man-made versions of maple seeds and other samaras have demonstrated very limited use. For example, researchers at the University of Maryland are designing and building robotic fliers that mimic samaras. See, e.g., http://www.avl.umd.edu/projects/projll-robotic-samara.html (confirmed on 19 Dec. 2010). Ned Allen, an aeronautical engineer, is leading a team at Lockheed Martin's Advanced Technology Lab (ATL) in the development of a simple maple seed-type samara device (the “ATL device”) for use in military and surveillance applications. See, e.g., http://www.atl.lmco.com/news/techfeatures/TODAY0706/TODAY_Nano.pdf (confirmed on 19 Dec. 2010). However, these and other known devices provide simple samara-like auto-rotating helicopters with similar flight characteristics that are literally based on the natural seeds, that is, turbulence-based in their lift creation and utilizing a simple “plate” wing and, in the case of the ATL device, a device that does not have a designated top or bottom surface to its wing. Thus, a need exists for simple, functional, well designed single-wing samara-like auto-rotating devices that utilize more efficient lift-producing airfoil sections in the wing and chassis geometry in order to increase payload, efficiency, predictability, and operational flexibility.